Spasticity, common in neurological disorders, is part of the upper motor neuron syndrome displaying increased tone, clonus, spasms, spastic dystonia and co-contractions. The impact of spasticity on the patient varies from a subtle neurological sign to severe spasticity causing pain and contractures. Upper limb spasticity (ULS) is the rapid contraction or shortening of the muscles in the arm causing abnormal muscle movements in the elbow, wrist and fingers. It has been reported that over 1 million Americans with traumatic injury to the brain or spinal cord, stroke, multiple sclerosis and cerebral palsy experience ULS. Tightly clenched fists, twisted wrist and elbow joints, and fixed arms in flexed positions result in extreme discomfort, pain and spasm. These symptoms may be aggravated by fatigue, stress, infections, and pain. Additionally, spasticity may lead to increased fatigue due to the extra energy expended to overcome tone during the movements involved in daily living activities.
Spasticity often requires both pharmacological and non-pharmacological interventions. The most commonly used pharmacological intervention is Baclofen, a muscle relaxant that works on nerves in the spinal cord. Oral Baclofen is commonly administered intrathecally through an implanted pumped and is often administered in conjunction with Botulinum toxin (Botox) and neurolytics (phenol) injections. Common side effects associated with Baclofen are drowsiness and muscle weakness. Furthermore, implanted pumps may cause post-implant complications including pump failure, infection, and lead displacement. While both Botulinum toxin and neurolytic injections have been shown to be effective in relieving spasticity both alone and in conjunction with oral interventions, both solutions are short-term and require retreatment every 3-6 months. Neurolytic injections impair nerve conduction by destroying a portion of a nerve and often cause additional necrosis of the neighboring sensory nerves, skin, muscles, blood vessels, and other soft tissues. In more severe cases, surgery can be performed to section nerves and relieve spasticity. These surgical procedures typically reduce upper-extremity spasticity but are associated with more severe, long-term adverse effects such as sensory disturbance and decrease in motor function in the affected area. It is clear that a nonsurgical, minimally invasive, effective approach to pain associated with ULS is desirable.